He graduated from the University of Texas School of Law with an LL.B. degree in 1942 and was admitted to the bar,[6][7] but soon afterwards joined the military for World War II. (When law schools accredited by the American Bar Association began requiring a bachelor's degree for admission to law school in the 1950s and 1960s, law schools began awarding the Juris Doctor (J.D.) degree rather than the LL.B.[8] As with most law school graduates of his era, Bentsen's LL.B. was amended to reflect award of the J.D.)[9]

After brief service as a private in intelligence work in Brazil, he trained to be a pilot and in early 1944 began flying combat missions in B-24s from Foggia, Italy with the 449th Bomb Group. At age 23, he was promoted to major and given command of a squadron of 600 men, overseeing the operations of 15 bombers, their crews, and their maintenance units. He was promoted to lieutenant colonel before being discharged in 1947.

Bentsen flew thirty-five missions against many heavily defended targets, including the Ploesti oil fields in Romania, which were critical to the Nazi war production. The 15th Air Force, which included the 449th Bomb Group, destroyed all petroleum production within its range, eliminating about half of Nazi Germany's sources of fuel. Bentsen's unit also flew against communications centers, aircraft factories and industrial targets in Germany, Italy, Austria, Czechoslovakia, Hungary, Romania, and Bulgaria. Bentsen participated in raids in support of the Anzio campaign and flew missions against targets in preparation for the landing in southern France. He was shot down twice.[10]

After the war, Bentsen returned to his native Rio Grande Valley. He served the people of his home area from 1946 to 1955, first as Hidalgo County Judge (a largely administrative post as opposed to judicial duties).

Bentsen moved to Houston where he founded Consolidated American Life Insurance Company (Calico). He also served on the board of Lockheed Corporation as well as those of several oil and gas companies. He was successful in his business career, and became very secure financially. By 1970, he had become president of Lincoln Consolidated, a financial holding institution.

Bentsen upset incumbent Ralph Yarborough, a liberal icon, in a bruising primary campaign for the 1970 Texas Democratic Senatorial nomination. The campaign came in the wake of Yarborough's politically hazardous votes in favor of the landmark Civil Rights Act of 1964 and the Voting Rights Act of 1965 and his opposition to the Vietnam War. Bentsen made Yarborough's opposition to the war a major issue. His television advertising featured video images of rioting in the streets at the 1968 Democratic National Convention, implying that Yarborough was associated with the rioters. While this strategy was successful in defeating Yarborough, it caused long-term damage to Bentsen's relationship with liberals in his party.[14][15]

Bentsen's campaign and his reputation as a centrist Democrat served to alienate him not only from supporters of Ralph Yarborough, but from prominent national liberals, as well. Indeed, during the 1970 Senate race, the Keynesian economist John Kenneth Galbraith endorsed George H. W. Bush, arguing that if Bentsen were elected to the Senate, he would invariably become the face of a new, more moderate-to-conservative Texas Democratic Party and that the long-term interests of Texas liberalism demanded Bentsen's defeat. Nevertheless, later that year, Bentsen went on to win the general election against Congressman and future President Bush, whom Bentsen beat convincingly.

Beginning in 1974, Bentsen campaigned for the Democratic Party's 1976 presidential nomination. In 1974 he visited 30 states and raised $350,000 at a single fundraiser in Texas. Bentsen formally announced his candidacy on February 17, 1975, and in the early part of that year he had already raised over $1 million for his campaign; only George Wallace of Alabama and Henry M. "Scoop" Jackson of Washington had raised more money by that point. Bentsen did not organize effectively on a national level, and many observers believed the freshman senator was running without any real hope of winning the nomination, hoping instead to secure a vice-presidential nomination.

Wallace and Jackson were considered to be the two main contenders for the moderate to conservative voters to whom Bentsen would appeal; early in the campaign few foresaw Jimmy Carter of Georgia also effectively appealing to that group.

By October 1975 Bentsen, generating little national attention or significance in the polls, scaled back his campaign to a limited effort in areas of 8 to 10 states, hoping for a deadlocked convention. In the first state contest Bentsen vigorously contested, Mississippi, he managed only 1.6% of the vote. Two weeks later Bentsen staked the remainder of his campaign and resources in neighboring Oklahoma but finished third with only 12%. A few days later Bentsen shut down his national campaign, staying in the race only as a favorite son in Texas. However, in the May 1, 1976, primary Jimmy Carter won 92 of Texas's 98 delegates. The eventual nominee and president, Carter was later quoted as saying he had expected a much stronger showing by Bentsen but that Bentsen's failure to campaign nationally had ended his hopes.

Firmly ensconced in Washington, Bentsen was overwhelmingly re-elected to the Senate in 1976, 1982, and 1988. He defeated sitting Republican congressmen from safe House seats in all four of his Senate elections, including Bush in 1970. In 1976, he ended the career of Alan Steelman of Dallas. In 1982, he defeated James M. Collins of Dallas, who had first dispatched the strongly conservativeState SenatorWalter Mengden of Houston in the Republican primary. In 1988, he defeated Beau Boulter of Amarillo. Bentsen was also on the ballot as the Democratic vice presidential nominee that year; he could seek both offices under the 1960 "Johnson law" in Texas.

Bentsen's early reputation as a conservative evolved over the years. His solid support for civil rights, the Equal Rights Amendment, environmental protection and preservation, and pro-choice policies was balanced by his endorsement of public school prayer, capital punishment, tax cuts, and deregulation of industry. While his record on social issues was progressive, he generally supported business interests in the arena of economic policy and swiftly rose to become a power to be reckoned with on the Senate Finance Committee. He came to be viewed as a moderate Democrat.

Bentsen was on Walter Mondale's short list of seven or eight possible vice presidential candidates in 1984 and was the only southerner and one of three white males considered. In the end, Mondale chose New York U.S. Representative Geraldine Ferraro as his running mate.

In 1988 GovernorMichael Dukakis (Massachusetts) chose Bentsen to be his running mate in that year's presidential election, beating out Ohio Senator John Glenn, who was considered the early favorite. Bentsen was selected in large part to try to lure away the state of Texas and its electoral vote for the Democrats, even with fellow Texan George H. W. Bush at the top of the Republican ticket. Because of Bentsen's status as something of an elder statesman who was more experienced in electoral politics, many believed Dukakis's selection of Bentsen as his running mate was a mistake in that Bentsen, number two on the ticket, appeared more presidential than did Dukakis. One elector in West Virginia even cast a ballot for him rather than Dukakis, giving Bentsen one electoral vote for President.[16] The Dukakis-Bentsen ticket was the first to feature a Massachusetts presidential and Texas vice-presidential candidate since John F. Kennedy and Lyndon B. Johnson were running mates in 1960.

Bentsen was responsible for one of the most memorable moments of the campaign during his televised debate with Republican vice presidential nominee Dan Quayle. In answering a question about his experience, Quayle stated that he had as much political experience as John F. Kennedy had when he ran for the presidency. Bentsen retorted, "Senator, I served with Jack Kennedy. I knew Jack Kennedy. Jack Kennedy was a friend of mine. Senator, you're no Jack Kennedy."[17] Quayle replied, "That was really uncalled for, Senator." Bentsen responded, "You're the one that was making the comparison, Senator."[18] Peter Goldman and Tom Mathews wrote in The Quest for the Presidency 1988 that Bentsen "was the forgotten man" of the campaign until the exchange with Quayle. Thereafter, his "gray solidarity" was "made luminescent by the pallor of the other three men. However, there have been questions raised as to how well Bentsen really knew Kennedy. Some have claimed they only had a nodding acquaintance." Bentsen had in fact considered in advance how to respond, because Congressman Dennis E. Eckart, who played Quayle in Bentsen's rehearsals, knew that Quayle had previously compared himself to Kennedy, so he worked it into Bentsen's debate preparation.[10][19]

The Dukakis-Bentsen ticket lost the election. Bentsen was unable to swing his home state, with 43 percent of the Texas vote going for the Dukakis ticket while Bush and Quayle took 56 percent, despite the fact that Bentsen was simultaneously re-elected to the United States Senate with 59 percent of the vote.[20]

Bentsen considered running for president in 1992, but he, along with many other Democrats, backed out because of Bush's apparent popularity following the successful Gulf War (Bush ended up losing the election to Bill Clinton).[21]

In early December 1994, Bentsen announced his resignation as Secretary of the Treasury. Before election day he had discussed with President Clinton that he was not prepared to stay in office until 1996. He was succeeded in the position by Robert Rubin.[25]

In 1995, former British Prime Minister Margaret Thatcher said in an interview with Larry King when asked which Democrats she admired: "I like Lloyd Bentsen very much indeed, I was sad when he resigned. He's a real marvelous politician, a person of great dignity, a person we can look up to respect and like as well."[26]

In 1998, Bentsen suffered two strokes, which left him needing a wheelchair for mobility. In 1999 President Clinton awarded Bentsen the Presidential Medal of Freedom, one of the nation's highest honors given to civilians. He appeared in the summer of 2004 at the portrait unveilings at the White House of former President Bill Clinton and former First Lady Senator Hillary Rodham Clinton.

Bentsen died on May 23, 2006, at his home in Houston at the age of 85. He was survived by his wife, the former Beryl Ann Longino, three children, and seven grandchildren. His memorial service was held on May 30 at the First Presbyterian Church of Houston, where Bentsen and his wife had been members for many years, and was presided by his then pastor, William Vanderbloemen.[27] He is interred in Forest Park Lawndale Cemetery. Former president Bill Clinton, who was a close friend, delivered a eulogy.[28]

As a freshman Senator, Bentsen guided to passage the Employee Retirement Income Security Act (ERISA), a long-stalled pension reform bill providing federal protections for the pensions of American workers. He also championed the creation of Individual Retirement Accounts (IRAs), legislation improving access to health care for low income women and children, and tax incentives for independent oil and gas producers to reduce dependence on foreign oil. In recognition of his success in securing federal funding, two hundred seventy miles of U.S. Highway 59, from I-35 to I-45 in Texas (between Laredo and Houston, respectively), are officially named Senator Lloyd Bentsen Highway.

As a primary architect of the Clinton economic plan, Bentsen contributed to a $500 billion reduction in the deficit, launching the longest period of economic growth since World War II. More than 5 million new jobs were created during his tenure as Secretary.[23]

His legacy also includes many water, wastewater and other infrastructure projects in the impoverished Colonia of south Texas, the preservation of natural areas across the state, and major funding for medical facilities too numerous to list.

Bentsen's retort to Vice President Dan Quayle during the 1988 Vice Presidential Debate, "You're no Jack Kennedy.", has entered the lexicon as a widely used phrase to deflate politicians who are perceived as thinking too highly of themselves. Bentsen is also known for coining the term astroturfing.

Bentsen's family continues to be active in politics. His nephew, Ken Bentsen, Jr., was a U.S. Representative (D) from 1995 to 2003 in Texas's 25th District, and a U.S. Senate candidate in 2002. His grandson, Lloyd Bentsen IV, served on John Kerry's advance staff during Kerry's 2004 campaign for the presidency of the United States.